Barrel Twist: Over Stabilize?

[snakyjake]

I was reading something about 1:7 "over stabilizing" a 5.56 55 gr bullet, and not optimum.

I also thought all that was needed is to choose the fastest twist rate necessary for the bullet weight. So a 1:7 would stabilize the heavier bullets, and still stabilize the lighter bullets too. But apparently a 1:7 would "over stabilize" a lighter 55 gr bullet, and this would not be "ideal" (for what?).

What does it mean for a bullet to be "over stabilized"? I figure the bullet is either unstable or stable.

[5pins]

I have shot lots of 55gr bullets in plenty of 1/7 twist barrels with good results. So no it will not “over stabilize”. How very light varmint bullets with thin jackets can disintegrate after exiting the muzzle.

[warpedcamshaft]

I've shot many thousands of 55 grain FMJ rounds out of several 1/7 twist guns, and have not seen issues with accuracy.

A recent example: American Eagle 5.56 M193 holding 3-4 inch 5 shot groups out to 200 yards out of a Daniel Defense and a Palmetto experimental build with an FN barrel.

I've also fired a bunch of the Federal bulk pack 50 grain HP rounds a while back out of 1/7 barrels and had good results at 100-200 yards.

[Unobtanium]

Just shot some 40gr through my 1/7. That, and wolf were the most accurate that day.

[That Guy]

From what I've read from the Internet, over stabilization *may* be an issue at longer ranges, but not at 100 or 200 yards.

(How much of an issue? And starting from what range?)

Or, it may not be. I'm looking forward to hearing from the resident experts on this topic.

[DocGKR]

No, you cannot "overstabilize", although bullets with fragile construction can be spun apart with fast twists (think 40 gr Blitz from a new 1/7 twist AR15 barrel that still has sharp rifling).

Many of our Nation's finest long range shooters have gone to using much faster twist barrels that traditionally done in the past.

For example, when I first shot Hi-Power in the early 1980's, most barrels were 1/11, we then went 1/10--now I would not even think about purchasing a .308, particularly one with a shorter barrel, unless it was a 1/8 or faster. Folks like Todd Hodnett and Buford Boone have been doing extensive research on this area and the results are quite conclusive.

[DamonL]

No, you cannot "overstabilize", although bullets with fragile construction can be spun apart with fast twists (think 40 gr Blitz from a new 1/7 twist AR15 barrel that still has sharp rifling).

Many of our Nation's finest long range shooters have gone to using much faster twist barrels that traditionally done in the past.

For example, when I first shot Hi-Power in the early 1980's, most barrels were 1/11, we then went 1/10--now I would not even think about purchasing a .308, particularly one with a shorter barrel, unless it was a 1/8 or faster. Folks like Todd Hodnett and Buford Boone have been doing extensive research on this area and the results are quite conclusive.

This is timely information. I am looking to rebarrel a .308 bolt gun to 20 inches and the common recommendations that I can find are for 1-10 and 1-12 twist. How fast a twist would you go? Pac Nor lists twists as fast as 1-4 and 1-7.

[DocGKR]

How far are you shooting? What are you shooting at? What bullets are you using?

[DamonL]

The only range I have access to is 100 yds. And it is paper targets. I have a case of IMI match ammo to burn with 168gr bullets.

[1slow]

When I was talking with long range shooters some years ago, I was told that the following needed to be looked at to get the correct rifling twist for stability.
Length of bullet, this often co-varies with weight, but a copper bullet that is as long as a copper jacket lead bullet may require the same rifling twist even though it is lighter.
Velocity, the more velocity at a given rifling twist the more projectile rpm and thus more stability. A 30-378 with the same twist rate as a 30-30 will generate more projectile rpm. Kind of an extreme example but illustrative.

These long range guys said you start with the following series of questions:
What desired impact effect, leads to what bullet, what velocity, what rifling twist to stabilize the bullet, what cartridge case gives the required capacity to generate the desired velocity, what barrel length, what action, etc...
Basically they started with a desired end state of a certain projectile at a certain velocity and then figured what it took to get there.
My understanding is this is how the .338 Lapua was developed. Started as .30-416 Rigby, case was shortened .200 inch and made stronger near the base. I read the idea was to have a bullet that was still supersonic at a mile and would shoot through people easily.